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AES Energy StorageA plant in Johnson City, N.Y., where batteries are used to store energy. AES Energy Storage proposes to furnish a bigger battery installation for the Long Island Power Authority.

When the Long Island Power Authority said last summer that it was going to need new power capacity in the next few years, most people assumed that meant new generating stations or new transmission cables. But of the 16 companies that submitted proposals, one, AES Energy Storage, took an entirely different tack: it proposed batteries.

When all is said and done, batteries are not a source of energy; in fact, they consume it. For every 10 kilowatt-hours put into a battery, only about nine come back out. The battery is a little like a savings account at a bank, but with a negative interest rate. Still, withdrawals are possible at times when they are most useful.

Batteries are a temporary source of energy and power, with the instantaneous ability to meet load and do work. AES is proposing the use of a 400-megawatt battery, with the same output as a medium-size natural gas plant, that can operate for four hours. It would be about 10 times larger than the biggest grid-connected battery system now in service.

AES said the battery would also be a cleaner energy choice. That’s because the alternative would probably be new simple-cycle natural gas plants, which are relatively low in efficiency and have a high output of carbon dioxide and conventional pollutants per kilowatt-hour.

Batteries, on the other hand, could be charged at night using relatively cheap capacity from Long Island’s most efficient generators, combined cycle gas plants. Those use about 7,000 B.T.U.’s of energy per kilowatt-hour, compared with 10,000 or 11,000 for the simple-cycle plants.

Can a battery qualify if the utility wants power?

In fact, in the complicated world of the electric grid, batteries can do some jobs better than generation stations. One is providing a service called spinning reserve. At a power plant, that means spinning a turbine and burning fuel, but not actually making any energy, sitting in standby in case more power is suddenly needed. A battery can sit at the ready without actually spinning or using fuel.

Another is frequency regulation. Alternating current is supposed to change directions 60 times per second, but in reality is always just a little faster or a little slower than that. Plants that provide frequency regulation will add or subtract energy at precise intervals to keep the number of alternations near 60.

Power plants that do this work get extra wear and tear, and modern gas-fired turbines are not as good for that job as old-fashioned steam plants were. Batteries, though, can take up the slack.

John Zahurancik, vice president of operations and deployment at AES, pointed out that getting permission to build batteries is easier than getting the go-ahead to build more power plants. No new permits for air emissions or water consumption would be needed, for example, he said.

The Long Island Power Authority said it was just beginning to evaluate the responses to its request for proposals, which was issued last August. It has not said which submissions met its terms and will be evaluated, and whether proposals for energy storage can compete. Officials there also declined to say whether any of the other bids were submitted by storage companies.

AES already operates an 8-megawatt battery installation in Johnson City, N.Y., near Binghamton and a 12-megawatt system in Chile. It is building a 32-megawatt system in West Virginia adjacent to a 97-megawatt wind farm. Batteries paired with wind farms can smooth out the wind turbines’ highly variable output.

The company’s Long Island proposal is still in an early phase; AES has not, for example, chosen precisely what type of battery it would use.